This invention relates generally to the field of gravity responsive or attitudinal switches, where the switch is operated by movement of the switch relative to true vertical, such that the position or attitude of the switch determines its operational status, for example, whether it is on/off or open/closed. More particularly, the invention relates to such switches which include a liquid element within a housing, where the position of the liquid element determines the operational status of the switch, usually in conjunction with the liquid element either completing or not completing an electrical circuit between a pair of contacts.
Gravity responsive or attitudinal switches, often referred to a tilt switches or mercury switches, are well known. A typical switch comprises a sealed chamber retaining a ball or bead of liquid mercury, a highly electrically conductive material which remains liquid at temperatures above xe2x88x9239 degrees C. The liquid mercury bead is a gravity responsive element, in that it will always occupy the lowermost position within the chamber as the chamber is moved, rotated, tilted, etc. A pair of contacts or leads, typically metal wires, are inserted through the body of the switch so that ends of the contacts are disposed within the chamber at a place where the liquid mercury bead can touch both contacts, with the contacts separated by a gap which is smaller than the general diameter of the liquid mercury bead. The contacts are part of a powered electrical circuit which is to be controlled by the switch. When the attitude of the switch is such that the mercury connects the two contact ends, a circuit is completed and the switch is in the on or closed status. When the attitude of the switch is such that the mercury does not bridge the gap between the two contact ends, the circuit is not completed and the switch is in the off or open status.
Although liquid mercury is an excellent material in terms of its ability to remain cohesive, i.e., to remain in the shape of a bead rather than spreading onto a surface, and in its ability to conduct electricity, it is a highly toxic material and extremely hazardous if improperly released into the environment. Misuse of mercury or its vapors can cause animal and human deaths. For this reason, it is highly desirable that gravity responsive switches be developed which do not rely on mercury.
It is an object of this invention to provide a gravity responsive or attitude switch which is capable of actuating an electric circuit, and thus in turn capable of controlling any operational function, mechanical or electronic, which does not require the use of highly conductive liquids, such as liquid mercury, as the gravity responsive element. It is a further object of this invention to provide such a switch where the gravity responsive member is a first or bead liquid which is immiscible in a second or carrier liquid, and where the surface tension of the bead liquid is such that the bead liquid retains a bead or ball-like shape within the carrier liquid, and further where the weight, density or specific gravity of the bead liquid is greater than that of the carrier liquid, so that the bead liquid will reside at the lowermost position relative to the carrier liquid, i.e., such that the bead liquid will sink within the carrier liquid. It is a further object to provide such a switch where the bead liquid gravity responsive member and the carrier liquid have differing electrical resistivity values. It is a further object to provide such a switch having at least a pair of contacts separated by a gap and disposed so as to contact the bead liquid, the carrier liquid, or both, dependent on the alignment, orientation or positioning of the switch. It is a further object to provide such a switch where the change in electrical, resistivity of the circuit containing the contacts is sensed and measured, such that the difference in resistivity sensed when the bead liquid member connects the gap between the contacts relative to the resistivity when the carrier liquid is in contact with the contacts determines the status of the switch and is used to actuate or de-actuate an operational electrical circuit.
The invention is a gravity responsive attitudinal switch used to control an operational electrical circuit, where the operative condition or status of the switch is dependent on its orientation relative to true vertical, such that in a certain position or positions the switch is xe2x80x9conxe2x80x9d or creates a closed circuit in the operational circuit, while in another position or positions the switch is xe2x80x9coffxe2x80x9d or creates an open circuit in the operational circuit. In general, the switch comprises a sealed housing defining an internal walled chamber, with any number of plural electrical contacts being disposed through or within the housing so that the contact ends extend to or into the chamber. The contacts may be formed as discrete members or member pairs or as continuous single or paired tracks which are exposed on the surface of the chamber or suspended within the interior of the chamber, and the chamber itself may be formed with a conductive wall to define a contact. Disposed within the chamber is a first or bead liquid and a second, or carrier liquid, where the two liquids have different electrical resistivity values. The bead liquid is immiscible in the carrier liquid and its surface tension is such that it preferably forms a bead or ball-like shape within the carrier liquid. The bead liquid is heavier than the carrier liquid, such that the bead liquid will reside at the bottom of the carrier liquid and at the lowermost portion of the chamber. The position of the contacts and the size of the bead liquid is such that the bead liquid is able to bridge the gap between contacts. The contacts are part of an electrical or electronic sensing circuit having means to sense the difference in resistivity of the bead liquid versus the resistivity of the carrier liquid, such that the operative status of the switch is determined by the value of the resistance detected in the sensing circuit.